1. Technical Field of the Invention
The present invention relates generally to a fuel injection system which may be employed with automotive internal combustion engines to learn a deviation of the quantity of fuel actually sprayed by a fuel injector from a target quantity to produce a correction value for correcting an on-duration for which the fuel injector is to be opened to spray the fuel desirably, and more particularly to such a fuel injection system designed to specify malfunctions occurring in the system.
2. Background Art
There are known fuel injection systems for diesel engines which are designed to spray a small quantity of fuel into the engine (usually called a pilot injection) prior to a main injection of fuel in order to reduce combustion noise or NOx emissions. However, a deviation of the quantity of fuel actually sprayed from a fuel injector from a target quantity in the pilot injection will result in a decrease in beneficial effects of the pilot injection.
In order to avoid the above problem, Japanese Patent First Publication No. 2005-155360 proposes a learning control system which is activated when the diesel engine is decelerating, and no fuel is being sprayed into the diesel engine. Specifically, the learning control system instructs a fuel injector to spray a single jet of a target quantity of fuel into the diesel engine, samples a resulting change in speed of the engine to calculate the quantity of fuel actually sprayed from the fuel injector, and determines a correction value for an injection duration for which the fuel injector is to spray the fuel (i.e., an on-duration for which the fuel injector is opened) based on a difference between the target quantity and the actually sprayed quantity of the fuel (which will also be referred to as an actual injection quantity below).
The fuel injection system with the above type of learning control function ensures the accuracy in injecting a desired quantity of fuel into the diesel engine, for example, in the pilot injection event, but however, it is not designed to identity the cause of an error in learned actual-to-target quantity deviation (i.e. the correction value).